Recent years have seen the development of voice processing apparatuses, such as mobile phones, teleconferencing systems, and telephones equipped with hands-free talking capability, that record voices by using a plurality of microphones. For such voice processing apparatuses, developing technologies for the voices recorded, attenuating voice coming from any direction other than a specific direction and thereby making voice coming from the specific direction easier to hear has been proceeding (refer to Japanese Laid-open Patent Publication No. 2007-318528 and Japanese Laid-open Patent Publication No. 2010-176105, for example).
For example, Japanese Laid-open Patent Publication No. 2007-318528 discloses a directional sound recording device which converts a sound received from each of a plurality of sound sources, each located in a different direction, into a frequency-domain signal, calculates a suppression coefficient for suppressing the frequency-domain signal, and corrects the frequency-domain signal by multiplying the amplitude component of the frequency-domain signal of the original signal by the suppression coefficient. The directional sound recording device calculates the phase components of the respective frequency-domain signals on a frequency-by-frequency basis, calculates the difference between the phase components, and determines, based on the difference, a probability value which indicates the probability that a sound source is located in a particular direction. Then, the directional sound recording device calculates, based on the probability value, a suppression coefficient for suppressing the sound arriving from any sound source other than the sound source located in the particular direction.
On the other hand, Japanese Laid-open Patent Publication No. 2010-176105 discloses a noise suppressing device which isolates sound sources of sounds received by two or more microphones and estimates the direction of the sound source of the target sound from among the isolated sound sources. Then, the noise suppressing device detects the phase difference between the microphones by using the direction of the sound source of the target sound, updates the center value of the phase difference by using the detected phase difference, and suppresses noise received by the microphones by using a noise suppressing filter generated using the updated center value.